The present disclosure relates to semiconductor processing methods, and particularly to a method of enhancing the etch rate of a silicon etch process through etch chamber pretreatment.
High aspect ratio deep silicon etch techniques are a key enabling technology for implementing through silicon via structures and three-dimensional integration of multiple semiconductor substrates. State of the art deep silicon etch utilizes a time modulated etch process, which is typically referred to as a “Bosch” process.
The Bosch process employs alternating cycles of etching employing a SF6 gas and polymer deposition employing a passivation gas such as C4F8, which is a fluorocarbon gas that does not include hydrogen. The Bosch process provides a reasonable level of anisotropy required for forming high aspect ratio structures. However, the Bosch process, as known in the art, has several limitations. Attempts to increase the etch rate of the Bosch process results in roughening of sidewalls and the bottom surface of the trench due to reduction in the thickness of the passivation layer. Further, sidewall scalloping and increased undercut in the trench structure accompanies attempts to increase the etch rate of the Bosch process.
In an alternative to the Bosch process, Cryogenic process or Non switching process, known as namely Non Bosch process is proposed. The feature of Non Bosch process is that etching and passivation are carried out in a continuous process until the entire silicon feature is etched, which enables to etch silicon features without scalloped sidewall. The etching gas for non-Bosch processes is SF6, and passivation gases are usually O2 or HBr or fluorocarbon gas such as C4F8 or hydro fluorocarbon gas such as CH3F, CHF3. For example, when using O2 as the passivation gas, a layer of SiOxFy wherein x and y is a positive integer is formed on the sidewall of the silicon feature under around −100 degrees Centigrade, which is more resistant to etch by SF6 than the silicon substrate.
Disadvantages of Non Bosch process are lower etch rate, temperature control issue and narrow process control margin rather than Bosch process. Attempts to increase the etch rate of the Non Bosch process results in roughening of sidewalls and the bottom surface of the trench due to reduction in the thickness of the passivation layer as well as Bosch process.
Thus, the etch rate of the Bosch or Non Bosch process as known in the art cannot be increased without deleterious effect on the etch profile of the trenches formed by the Bosch or Non Bosch process. The requirement of smooth sidewalls and bottom surfaces as well as controlled undercut in the profile of the trenches limits the etch rate of the Bosch process, and in turn, limits the throughput of etch chambers that perform the Bosch or Non Bosch process. The productivity of etch chambers performing the Bosch or Non Bosch process is thus limited by the etch rate of the Bosch process.